Title: High Energy Density Li-ion Cells for EV’s Based on Novel, High Voltage Cathode Material Systems

Abstract

This Li-ion cell technology development project had three objectives: to develop advanced electrode materials and cell components to enable stable high-voltage operation; to design and demonstrate a Li-ion cell using these materials that meets the PHEV40 performance targets; and to design and demonstrate a Li-ion cell using these materials that meets the EV performance targets. The major challenge to creating stable high energy cells with long cycle life is system integration. Although materials that can give high energy cells are known, stabilizing them towards long-term cycling in the presence of other novel cell components is a major challenge. The major technical barriers addressed by this work include low cathode specific energy, poor electrolyte stability during high voltage operation, and insufficient capacity retention during deep discharge for Si-containing anodes. Through the course of this project, Farasis was able to improve capacity retention of NCM materials for 4.4+ V operation, through both surface treatment and bulk-doping approaches. Other material advances include increased rate capability and of HE-NCM materials through novel synthesis approach, doubling the relative capacity at 1C over materials synthesized using standard methods. Silicon active materials proved challenging throughout the project and ultimately were the limiting factor in the energy densitymore » vs. cycle life trade off. By avoiding silicon anodes for the lower energy PHEV design, we manufactured cells with intermediate energy density and long cycle life under high voltage operation for PHEV applications. Cells with high energy density for EV applications were manufactured targeting a 300 Wh/kg design and were able to achieve > 200 cycles.« less

@article{osti_1425982,
title = {High Energy Density Li-ion Cells for EV’s Based on Novel, High Voltage Cathode Material Systems},
author = {Kepler, Keith D. and Slater, Michael},
abstractNote = {This Li-ion cell technology development project had three objectives: to develop advanced electrode materials and cell components to enable stable high-voltage operation; to design and demonstrate a Li-ion cell using these materials that meets the PHEV40 performance targets; and to design and demonstrate a Li-ion cell using these materials that meets the EV performance targets. The major challenge to creating stable high energy cells with long cycle life is system integration. Although materials that can give high energy cells are known, stabilizing them towards long-term cycling in the presence of other novel cell components is a major challenge. The major technical barriers addressed by this work include low cathode specific energy, poor electrolyte stability during high voltage operation, and insufficient capacity retention during deep discharge for Si-containing anodes. Through the course of this project, Farasis was able to improve capacity retention of NCM materials for 4.4+ V operation, through both surface treatment and bulk-doping approaches. Other material advances include increased rate capability and of HE-NCM materials through novel synthesis approach, doubling the relative capacity at 1C over materials synthesized using standard methods. Silicon active materials proved challenging throughout the project and ultimately were the limiting factor in the energy density vs. cycle life trade off. By avoiding silicon anodes for the lower energy PHEV design, we manufactured cells with intermediate energy density and long cycle life under high voltage operation for PHEV applications. Cells with high energy density for EV applications were manufactured targeting a 300 Wh/kg design and were able to achieve > 200 cycles.},
doi = {10.2172/1425982},
journal = {},number = ,
volume = ,
place = {United States},
year = {2018},
month = {3}
}

The chief thrust of the research has been directed towards the evaluation of polyacetylene (CH)/sub x/, the prototype conducting polymer as an electrode-active material in novel, rechargeable batteries employing nonaqueous electrolytes. The p-doped material, ((CH/sup +y/)A/sub y//sup -/)/sub x/, (where A/sup -/ is an anion) in conjunction with a Li anode, shows excellent discharge characteristics, e.g., very little change in discharge voltage with change in discharge current and a high power density. Its energy density is also good but it shows poor shelf life. When (CH)/sub x/ is used as a cathode (Li anode), which results in the formation ofmore » the n-doped polymer, (Li/sub y//sup +/(CH/sup -y/))/sub x/, during discharge, good discharge plateaus and power densities are obtained together with excellent shelf life and good recyclability. The energy density is, however only moderate. Cells employing an (M/sub y//sup +/(CH/sup -y/))/sub x/ (where M = Li, Na) anode and a TiS/sub 2/ cathode show very good discharge and recycling characteristics but their energy density is poor.« less

High-capacity and high-power nickel-based cathode materials have become the principal candidates for a lithium-ion energy storage system powering electrified transportation units. With high nickel content, the cathodes are of great interest for delivering the desired specific energy and energy density. However, the cells still suffer from fast capacity decay and low thermal-abuse tolerance to high voltage. At the highly delithiated state, the damage in the cell is mainly from severe parasitic reactions, including the oxygen evolution reaction in the cathode and oxidization of the organic electrolyte. These side reactions rapidly weaken the system's rate capacity and cyclability. Solutions are beingmore » sought to provide safe operation and practical application. Three strategies have proven to be encouraging choices: surface coating, a core-shell structure, and a concentration gradient structure. For each strategy, the material architecture, fabrication procedure, operation principle, advances, and challenges are discussed in this review. Furthermore, the prospects for further developments are also summarized.« less

Commercial Li-ion batteries typically use Ni- and Co-based intercalation cathodes. As the demand for improved performance from batteries increases, these cathode materials will no longer be able to provide the desired energy storage characteristics since they are currently approaching their theoretical limits. Conversion cathode materials are prime candidates for improvement of Li-ion batteries. On both a volumetric and gravimetric basis they have higher theoretical capacity than intercalation cathode materials. Metal fluoride (MFx) cathodes offer higher specific energy density and dramatically higher volumetric energy density. Challenges associated with metal fluoride cathodes were addressed through nanostructured material design and synthesis. A majormore » goal of this project was to develop and demonstrate Li-ion cells based on Si-comprising anodes and metal fluoride (MFx) comprising cathodes. Pairing the high-capacity MFx cathode with a high-capacity anode, such as an alloying Si anode, allows for the highest possible energy density on a cell level. After facing and overcoming multiple material synthesis and electrochemical instability challenges, we succeeded in fabrication of MFx half cells with cycle stability in excess of 500 cycles (to 20% or smaller degradation) and full cells with MFx-based cathodes and Si-based anodes with cycle stability in excess of 200 cycles (to 20% or smaller degradation).« less